A smartphone plays a more and more important role in our daily activities. It is more than a simple communication tool; is increasing its features which bring services for entertainment, lifestyle, health, education or business. In all those categories of application, it may be useful to pair smartphones for sharing information or resources like displays or sensors.
In some cases, it may be necessary to secure this pairing in order to avoid that a third device captures private data or prevents an application from working correctly.
Relating to the concern, different mechanisms exist to secure a device pairing.                The most used method is based on key sharing (PIN code, passphrase), like in Bluetooth technology.        Another method is to use the proximity to control the device which is currently pairing, for instance, with NFC which works using magnetic induction.        Another method for a controller device to identify a pairing device is to detect an event simultaneously with it. This is done, for instance, by making the devices touch each other.        A device A can authenticate to a device B, if the device B is equipped with a camera like in SiB (Seeing-is-Believing) method.        
In entertainment applications, the smartphone coupling allows to share and play content with other users in real time. Samsung provides such a service as Group Play, where several smartphones may be associated to display video with a bigger size.